JP4257988B2 - Purification method of ε-caprolactam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for purifying ε-caprolactam (hereinafter sometimes referred to as “lactam”). Specifically, the present invention relates to a method for purifying a lactam by hydrogenating a crude lactam containing impurities.
[0002]
[Prior art]
ε-Caprolactam is an organic product mainly used as a raw material for nylon-6, and is industrially produced by a Beckmann rearrangement reaction of cyclohexanone oxime (hereinafter sometimes referred to as “oxime”). There are several kinds of quality standard items in the product lactam that are almost common between manufacturers and users (see, for example, Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, A5, page 46). In order to satisfy these quality standards, As a method for purifying lactam, methods such as liquid-liquid distribution, distillation, crystallization, hydrogenation treatment, ion exchange, and activated carbon treatment have been studied and adopted.
Among these purification methods, the hydrogenation method is effective in reducing the PM value (quality standard relating to the content of impurities oxidized by potassium permanganate), and various methods have been reported in the past. For example, Japanese Patent Publication No. 32-6358 discloses a method of treating a crude lactam as an aqueous solution, and Japanese Patent Publication No. 46-23743 discloses a treatment of a crude lactam in an aromatic hydrocarbon solvent in the presence of an organic amine. Japanese Patent Application Laid-Open No. 3-135958 describes a method in which an aqueous solution of crude lactam is continuously treated by upflow under heat and pressure.
[0003]
[Problems to be solved by the invention]
The present inventor has particularly introduced tetrahydroazepin-2-ones (1,3,4,5-isomer, 1,3,4,7-isomer, 1,3,6,7-isomer and 1,5,5) as impurities. There are four types of 6,7-isomers; hereinafter, the hydrogenation treatment of crude lactams including “caprenolactams”) has been studied. In the conventional method, caprenolactams are Although it can be converted to lactam by hydrogenation and the PM value can be reduced, increase in VB (quality standard for volatile base) and acidification may be caused, which is not always sufficient.
An object of the present invention is to solve the above-mentioned problems and to provide a method for purifying lactam by a hydrogenation treatment method in which increase in VB and acidification are suppressed.
[0004]
[Means for Solving the Problems]
As a result of intensive studies, the present inventor has found that when a trace amount of oxygen is present or mixed in the hydrogen gas to be contacted in the hydrogenation treatment of the crude lactam, the lactam is oxidized despite the reduction conditions. The present inventors have found that adipic imide (hereinafter sometimes referred to as “ADI”) is by-produced, and that the greater the amount of ADI by-product, the greater the degree of VB increase and acidification. And by making oxygen concentration in this hydrogen gas below a specific amount, it discovered that the byproduct of ADI was suppressed and the increase in VB and acidification were suppressed, and came to complete this invention.
That is, the present invention provides a method for purifying ε-caprolactam, wherein when crude ε-caprolactam is contacted with hydrogen gas or a hydrogen-containing gas in the presence of a hydrogenation catalyst, the oxygen concentration in the gas is 1000 ppm by volume or less. It is concerned.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
In the present invention, as the crude lactam, those obtained by various reactions that produce lactams can be used. Examples of the reaction include oxime Beckmann rearrangement and 6-aminocaproic acid such as methyl 6-aminocaproate. Examples include cyclization reaction of esters, hydrolysis cyclization reaction of 6-aminocapronitrile, and the like. Especially, the method of this invention can be used suitably for the crude lactam obtained by the Beckmann rearrangement reaction of oxime.
[0006]
Examples of the Beckmann rearrangement reaction of oxime include those carried out under liquid phase conditions using acids such as sulfuric acid, fuming sulfuric acid, phosphoric acid and hydrochloric acid, boric acid catalysts, silica / alumina catalysts, solid phosphoric acid catalysts, Examples thereof include those carried out under gas phase conditions using a composite metal oxide catalyst, a zeolite catalyst such as a metallosilicate or silicalite. The method of the present invention can be applied to a crude lactam obtained by any Beckmann rearrangement reaction.
[0007]
As the crude lactam obtained by the Beckmann rearrangement reaction under liquid phase conditions of oxime, an oil phase obtained by mixing a base such as ammonia and water into the reaction solution and separating the mixture from oil to water may be used, A concentrate obtained by extracting lactam from the mixture or oil phase with an organic solvent such as benzene and concentrating the extract may be used, or a distillate obtained by distilling the oil phase or concentrate. May be used.
[0008]
As the crude lactam obtained by the Beckmann rearrangement reaction under the gas phase condition of the oxime, a condensate of the reaction gas may be used, or a concentrate obtained by concentrating the condensate may be used. A distillate obtained by distilling the condensate or concentrate may be used.
[0009]
As impurities contained in the crude lactam, depending on the preparation method, for example, remaining raw material oxime, caprenolactams, 1,2,3,4,6,7,8,9-octahydrophenazine (Hereinafter sometimes referred to as “OHP”), 1-methyl-4,5,6,7-tetrahydrobenzimidazole (hereinafter also referred to as “MTHI”), and the like. In the method of the present invention, the caprenolactam as an impurity can be converted into the target lactam by a hydrogenation treatment. Therefore, the crude lactam contains a relatively large amount of caprenolactam as an impurity, for example, 30 ppm or more. Even a thing can be used suitably.
[0010]
On the other hand, the content of impurities other than caprenolactam, such as oxime, OHP, and MTHI, in the crude lactam is preferably as low as possible, for example, oxime is 10 ppm or less, OHP is 10 ppm or less, and MTHI is 25 ppm or less. Therefore, it is preferable to use a crude lactam that has been purified by crystallization or the like before the hydrogenation treatment. When crystallization is performed using a solvent, examples of the solvent include aliphatic hydrocarbon solvents such as n-heptane and cyclohexane, and a mixed solvent can also be used as necessary. If the solvent used for crystallization is susceptible to hydrogenation, it is preferable to remove it as much as possible before subjecting it to a hydrogenation treatment. However, if the solvent is difficult to undergo hydrogenation, a small amount is added to the crystal. The hydrogenation treatment can be performed while the solvent is contained.
[0011]
The crude lactam can be hydrogenated by contacting it with hydrogen gas or a hydrogen-containing gas in the presence of a hydrogenation catalyst (hereinafter sometimes referred to as “catalyst”). Examples of the catalyst include group VIII transition metals such as nickel, palladium, platinum, ruthenium, and rhodium, and two or more of them can be used as necessary. The catalyst is preferably used as a supported catalyst supported on a suitable carrier. Examples of the carrier include activated carbon, alumina, silica, titania and the like. Among them, from the viewpoint of catalyst activity and catalyst life, those in which palladium is supported on the surface of activated carbon, and those in which platinum or ruthenium is co-supported are preferable, and an egg shell type catalyst is particularly preferable. When using a catalyst in which palladium is supported on activated carbon, the supported amount of palladium is usually 0.1 to 20% by weight, preferably 0.5 to 5% by weight, based on the entire supported catalyst. Also, if further platinum and Le ruthenium is used co-supported catalyst, the supported amount, relative to the entire supported catalyst, is usually 2 wt% or less. In addition, although the lifetime of a catalyst changes with conditions of the rough lactam to be used or a hydrogenation process, according to the method of this invention, it can also be made into 1 year or more.
[0012]
In the present invention, the oxygen concentration in the hydrogen gas or hydrogen-containing gas brought into contact with the crude lactam needs to be 1000 ppm (volume / volume, the same shall apply hereinafter) or less, preferably 500 ppm or less, more preferably 50 ppm or less. The higher the oxygen concentration, the greater the amount of ADI by-products, and the greater the degree of VB increase and acidification. An example of the relationship between the oxygen concentration and the by-product rate of ADI is as follows. Under the conditions of a batch system, a reaction temperature of 120 ° C., a reaction time of 1 h, and a hydrogen pressure of 0.3 MPa, the ADI production rate is the oxygen concentration. The result was almost proportional to the logarithm.
[0013]
In order to keep the oxygen concentration below a predetermined value, hydrogen gas that has been sufficiently purified is used, and the oxygen concentration is controlled so that it does not exceed a predetermined value due to air or the like entering the reaction system. There is a need. When a supported catalyst is used, it is preferable to pretreat the supported catalyst with an inert gas or hydrogen gas in advance in order to remove oxygen adsorbed and staying in the pores of the support.
[0014]
In the hydrogenation treatment, an organic solvent such as alcohol or water can be used as a solvent as necessary. The hydrogenation treatment may be performed in a batch format or a distribution format. When carried out in a flow mode, the crude lactam or a solution thereof may be circulated in an up flow with hydrogen gas, or may be circulated in a down flow, or the crude lactam or a solution thereof and hydrogen. Gas may be circulated countercurrently. Alternatively, the catalyst layer may be filled with hydrogen gas, and the reaction may be performed while the crude lactam or a solution droplet of the catalyst layer is allowed to flow down from the upper part of the catalyst layer. If the internal pressure is kept constant and the consumed hydrogen is replenished, the amount of hydrogen gas used can be suppressed, and the problem of hydrogen gas drift can be avoided. In either case of batch format or distribution format, it is preferable to pre-treat the catalyst with hydrogen gas in advance.
[0015]
The usage-amount of hydrogen gas is 0.0001 mol or more normally with respect to 1 mol of lactam in a crude lactam, Preferably it is the range of 0.001-0.1 mol. When caprenolactams are contained in the crude lactam, the caprenolactams and hydrogen gas in an equimolar amount or more are required. When the reaction is carried out in a circulation format, the hydrogen gas discharged without being used can be purified and reused as necessary.
[0016]
When the solvent is not used, the hydrogenation treatment temperature needs to be equal to or higher than the temperature at which the crude lactam melts, and is preferably in the range of 70 to 150 ° C. When a solvent is used, the temperature can be lowered to a temperature at which lactam does not precipitate from the solution. In addition, when carried out in a flow mode, the catalyst activity gradually decreases with time, so it is preferable to increase the temperature with a decrease in activity and maintain the catalyst activity at a certain level. Therefore, it is preferable to start at a relatively low temperature of 80 ° C. or lower initially and gradually increase the temperature.
[0017]
The pressure of the hydrogenation treatment is usually 0.05 to 10 MPa, preferably 0.1 to 1 MPa. In addition, the time for the hydrogenation treatment is usually in the range of 10 minutes to 2 hours in the case of a batch type, and in the case of a distribution type, usually as WHSV (the supply rate of crude lactam per kg of catalyst (kg / h)) 0.5~100h ^-1, preferably in the range of 1~10h ^-1.
[0018]
About the lactam after a hydrogenation process, when a solvent is included, a solvent can be removed by performing simple distillation. Even when no solvent is contained, it is preferable to perform simple distillation in order to remove catalyst-derived foreign matters and the like. As a result of the hydrogenation treatment, the caprenolactam content is usually 30 ppm or less, preferably 25 ppm or less, the PM value is usually 10 or less, preferably 7 or less, and the ADI content is usually 15 ppm or less, preferably Can obtain a purified lactam of 10 ppm or less.
[0019]
The method of the present invention can be employed as a method for purifying lactam in various lactam production methods. By including the step of purifying the lactam by the method of the present invention, a high-quality lactam can be produced.
[0020]
【Example】
Examples of the present invention will be described below, but the present invention is not limited thereto.
The GC analysis and the quality standard analysis were performed by the following methods.
<GC analysis>
The analysis was performed under the conditions of column: DB-WAX, temperature: 80 ° C. → 230 ° C., detection: FID, and the area percentage excluding the solvent was calculated. The detection limit of impurities is about 3 ppm.
<UV absorbance>
A 50% aqueous solution of lactam was placed in a 1 cm cell, water was used as a blank, and ultraviolet transmittance (%) at a wavelength of 290 nm was measured.
<Potassium permanganate value (PM value)>
To an aqueous solution in which 1 g of lactam was dissolved in distilled water to make 100 ml, 2 ml of 0.01N potassium permanganate aqueous solution was added and stirred. After 250 seconds from the addition of the aqueous potassium permanganate solution, the absorbance of light having a wavelength of 420 nm was measured at 25 ° C. (solution temperature). On the other hand, as a blank, 2 ml of 0.01N potassium permanganate aqueous solution was added to 100 ml of distilled water, stirred, and after 250 seconds had elapsed since the addition of the potassium permanganate aqueous solution, the absorbance of light having a wavelength of 420 nm was 25. Measured at ° C (solution temperature). The value obtained by subtracting the latter absorbance from the former absorbance and multiplying the value by 100 was defined as the potassium permanganate value (PM value).
<Free basicity (FB)>
About 2.5 g of lactam was added to 10 ml of water adjusted to pH 5.7 by adding 0.01 N sulfuric acid or sodium hydroxide aqueous solution to distilled water and stirred. The pH of the obtained solution was measured, and if the pH value was greater than 5.7, 0.01N sulfuric acid was added to the solution until the pH reached 5.7. The free basicity (FB; meq / kg) was calculated from the use amount of the added 0.01 N sulfuric acid v (ml), factor (f), and lactam weight w (g) used according to the following formula.
FB = 0.01 × v × f × 1000 / w
<Volatile basicity (VB)>
A distillation flask was charged with 5 g of lactam and 8 ml of a 20% aqueous sodium hydroxide solution and subjected to steam distillation, and the distillate was introduced into 5 ml of 0.01 N sulfuric acid aqueous solution. Steam distillation was terminated when the amount of distillate was 150 ml. The resulting solution was titrated with 0.01N aqueous sodium hydroxide using a methyl red-methylene blue mixed indicator. From the titration amount B (ml), the titration amount A (ml) in a blank test without lactam, the factor (f ′) of 0.01N sodium hydroxide aqueous solution, and the lactam weight w ′ (g) used, Basicity (VB; ppm) was calculated.
VB = [0.17 × (BA) × f ′ × 1000] / w ′
<Chromaticity (APHA)>
A 50% aqueous solution of lactam was placed in a 5 cm cell, water was used as a blank, the absorbance of light at 370 nm was measured, and converted to chromaticity using a calibration curve prepared in advance with a Hazen standard color solution.
[0021]
Reference example 1
99.20% purity lactam containing oxime: 496 ppm, MTHI: 181 ppm, caprenolactams: 430 ppm and OHP: 242 ppm was adjusted to 73 ° C. at 300 parts by weight per unit time, and the solvent [n-heptane / Cyclohexane = 3/1 (W / W)] was adjusted to 5.5 ° C., and 550 parts by weight per unit time, and the outer jacket was poured into a crystallization tank at 56 ° C. for crystallization. While stirring, the slurry was continuously introduced into a centrifugal decanter kept at 56 ° C. with an average residence time of 34 minutes, and solid-liquid separation was performed, and the solid phase was added with the solvent at 50 ° C. (120 parts by weight per unit time). Washed. As a result, 207 parts by weight of lactam per unit time was obtained as crystals. As a result of analysis, the solvent content was 1.7% by weight [n-heptane / cyclohexane = 1.75 (W / W)], and GC analysis (solvent As a result, the lactam was 99.98%, the oxime was 6 ppm, and the caprenolactams were 172 ppm. MTHI, OHP, and ADI were not detected.
[0022]
Reference example 2
Lactam prepared in the same manner as in Reference Example 1 was concentrated under reduced pressure. As a result of analyzing the obtained lactam, the solvent content was 0.1% by weight or less, and as a result of GC analysis (area percentage excluding the solvent), lactam: 99.9858%, caprenolactams: 129 ppm, Oxime, MTHI, OHP and ADI were not detected.
[0023]
Example 1
2% Pd / activated carbon catalyst (10-20 mesh) was charged with 207 parts by weight of the lactam obtained in Reference Example 1 and 0.0207 parts by weight of hydrogen with an oxygen concentration of 0.1 ppm per unit time. The catalyst layer was continuously supplied at 95 ° C. with WHSV = 2.6 h ⁻¹ . The obtained reaction mass was concentrated and distilled under reduced pressure to obtain lactam as a fraction. As a result of GC analysis of this lactam, lactam: 99.99% or more, caprenolactams: 1 ppm, and oxime, MTHI, OHP and ADI were not detected. Moreover, the quality specification analysis value of this lactam was UV absorbance: 92.0%, PM value: 1.1, APHA: 0.5, VB: 2.7, FB: 0.03.
[0024]
Example 2
A 200 ml SUS autoclave was charged with 1.8 g of a 2% Pd / C catalyst, the inside of the system was replaced with hydrogen having an oxygen concentration of 0.1 ppm, and the mixture was stirred at 120 ° C. for 1 hour at 100 rpm and then cooled. After the nitrogen substitution, 9 g of water and 90 g of the lactam obtained in Reference Example 2 were added thereto, and the system was substituted with hydrogen having an oxygen concentration of 0.1 ppm, and then 3.0 kg / cm ² (0.3 MPa) with this hydrogen. ) And stirred at 1000 rpm for 1 hour at 120 ° C. The reaction solution was pressure filtered under a nitrogen atmosphere to obtain a filtrate.
As a result of GC analysis (area percentage excluding the solvent) of this filtrate, lactam: 99.9981% and caprenolactams: 8 ppm, and no oxime, MTHI, OHP and ADI were detected. The filtrate was concentrated and distilled under reduced pressure to obtain lactam as a fraction. As a result of quality standard analysis of the lactam, UV absorbance: 99.2%, PM value: 0.25, APHA: 0.65, VB: 3.0 ppm, FB: 0.045.
[0025]
Comparative Example 1
In Example 2, instead of hydrogen having an oxygen concentration of 0.1 ppm, the same operation as in the previous stage of Example 2 was performed except that hydrogen having a nitrogen concentration of 3900 ppm and an oxygen concentration of 1050 ppm was obtained, thereby obtaining a filtrate.
As a result of GC analysis (area percentage excluding the solvent) of this filtrate, lactam: 99.9950%, caprenolactams: 8 ppm, ADI: 17 ppm, and oxime, MTHI and OHP were not detected. The filtrate was concentrated and distilled under reduced pressure to obtain lactam as a fraction. As a result of quality standard analysis of this lactam, UV absorbance: 98.6%, PM value: 1.43, APHA: 0.97, VB: 7.9, and FB shows a pH of less than 5.7. It was not possible to measure.
[0026]
Example 3
In Example 2, the same operation as in the previous stage of Example 2 was performed except that hydrogen having a nitrogen concentration of 1780 ppm and an oxygen concentration of 480 ppm was used instead of hydrogen having an oxygen concentration of 0.1 ppm to obtain a filtrate.
As a result of GC analysis (area percentage excluding the solvent) of this filtrate, lactam: 99.9926%, caprenolactams: 15 ppm, ADI: 8 ppm, and oxime, MTHI and OHP were not detected. The filtrate was concentrated and distilled under reduced pressure to obtain lactam as a fraction. As a result of quality standard analysis of the lactam, UV absorbance: 98.9%, PM number: 0.77, APHA: 1.02, VB: 5.6, FB: 0.013.
[0027]
Example 4
In Example 2, instead of hydrogen having an oxygen concentration of 0.1 ppm, the same operation as in the previous stage of Example 2 was carried out except that hydrogen having a nitrogen concentration of 160 ppm and an oxygen concentration of 50 ppm was used to obtain a filtrate.
As a result of GC analysis (area percentage excluding the solvent) of this filtrate, lactam: 99.9964%, caprenolactams: 9 ppm, ADI: 7 ppm, and oxime, MTHI and OHP were not detected. The filtrate was concentrated and distilled under reduced pressure to obtain lactam as a fraction. As a result of quality standard analysis of the lactam, UV absorbance: 98.7%, PM value: 0.56, APHA: 1.1, VB: 3.3, FB: 0.052.
[0028]
【The invention's effect】
According to the present invention, it is possible to perform a hydrogenation treatment under conditions where increase in VB and acidification are suppressed, and a lactam having a reduced PM value can be obtained.

Claims (6)

When the crude ε-caprolactam is brought into contact with hydrogen gas or a hydrogen-containing gas in the presence of a hydrogenation catalyst, the oxygen concentration in the gas is adjusted to 1000 ppm by volume or less , and the crude ε-caprolactam is purified by crystallization in advance. And a method for purifying ε-caprolactam, characterized by comprising tetrahydroazepin-2-ones . The content of cyclohexanone oxime in the crude ε-caprolactam is 10 ppm or less with respect to the crude ε-caprolactam, and 1,2,3,4,6,7,8,9-octahydrophenazine in the crude ε-caprolactam The content of 1-methyl-4,5,6,7-tetrahydrobenzimidazole in the crude ε-caprolactam is 10 ppm or less with respect to the crude ε-caprolactam. The purification method according to claim 1, which is 25 ppm or less .   The purification method according to claim 1 or 2, wherein the crude ε-caprolactam is obtained by a Beckmann rearrangement reaction of cyclohexanone oxime. The purification method according to any one of claims 1 to 3, wherein crystallization is performed using an aliphatic hydrocarbon solvent .   The purification method according to any one of claims 1 to 4, wherein the content of adipic imide in the purified ε-caprolactam is 15 ppm or less.   A method for producing ε-caprolactam, comprising a step of purifying ε-caprolactam by the purification method according to claim 1.